Brineworks, a Dutch cleantech company founded in 2023, has developed a groundbreaking electrolytic electrodialysis technology that serves a dual purpose: removing CO₂ from seawater and producing H₂. This innovative approach contributes significantly to ocean-based carbon removal efforts while simultaneously supporting the production of sustainable fuels.
(This article contains 4 diagrams and 1710 words.)
Challenges: carbon removal
Carbon dioxide (CO₂) emissions, primarily from human activities like fossil fuel combustion, deforestation, and industrial processes, are a major driver of climate change. Since the Industrial Revolution began in the late 18th century, over 1.5 trillion tonnes of CO₂ have been emitted globally, significantly increasing atmospheric concentrations of this greenhouse gas. In 2023, global average atmospheric CO₂ levels reached an unprecedented 419.3 parts per million (ppm).
China, the United States, and India are the largest CO₂ emitters, collectively responsible for a substantial portion of global emissions. China alone accounts for approximately 35% of global CO₂ emissions.
The rise in CO₂ levels is directly connected to global warming and climate change, as CO₂ traps heat in the atmosphere. This leads to increasing temperatures, altered weather patterns, and more frequent extreme weather events. International climate agreements, such as the Paris Agreement, aim to limit global warming to well below 2 ºC above pre-industrial levels, necessitating significant reductions in CO₂ emissions.
Oceans, covering over 70% of Earth's surface, are the planet's largest carbon sink, absorbing about 40% of human-emitted CO₂. They play a crucial role in buffering climate change by locking atmospheric CO₂ in the form of stable bicarbonate ions (HCO₃⁻) and solid precipitates (CaCO₃ and MgCO₃) through a series of chemical reactions:
CO₂ + H₂O ⇆ H₂CO₃
H₂CO₃ ⇆ H⁺ + HCO₃⁻
HCO₃⁻ ⇆ H⁺ + CO₃²⁻
CO₃²⁻ + Ca²⁺ ⇆ CaCO₃↓
CO₃²⁻ + Mg²⁺ ⇆ MgCO₃↓
Direct Ocean Capture (DOC) is a carbon removal technology that utilizes seawater to produce acid and alkaline solutions via an electrochemical process.
The acid solution is used to extract and capture CO₂ directly from seawater by converting HCO₃⁻ ions into CO₂ gas, according to the following chemical reactions:
H⁺ + HCO₃⁻ → H₂CO₃
H₂CO₃ → CO₂↑ + H₂O
This process is more efficient and cost-effective compared to the Direct Air Capture (DAC), because at its current average pH of 8.1, seawater contains 150 times more CO₂ than an equal volume of the air.
The alkalinity solution with safe pH is returned to seawater to increase its local alkalinity, promoting further CO₂ dissolution and conversion to stable bicarbonate ions.
CO₂ + OH⁻ → HCO₃⁻
This process, known as Ocean Alkalinity Enhancement (OAE), enhances the ocean's natural carbon sequestration ability.
Brineworks Technology
Direct Ocean Capture (DOC) requires the use of alkaline and/or acidic solutions, typically sodium hydroxide (NaOH) and hydrochloric acid (HCl), which can be produced through existing technologies such as chlor-alkali electrolysis and bipolar membrane electrodialysis.
The chlor-alkali process is a significant industrial method for producing sodium hydroxide (caustic soda) via electrolysis of sodium chloride (NaCl) solutions. Traditionally, this process has utilized brine, a concentrated solution of salt, but there is growing interest in using seawater as a more sustainable feedstock.
A chlor-alkali electrolytic cell utilizes a single cation-exchange membrane to separate the anode and cathode compartments, as depicted in the diagram below.
An electric current is passed through an aqueous solution of NaCl or seawater. At the anode (positive electrode), chloride ions (Cl⁻) are oxidized to produce chlorine gas (Cl₂). At the cathode (negative electrode), water (H₂O) is reduced to produce hydrogen gas (H₂) and hydroxide ions (OH⁻). The overall reaction is
2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH
The chlor-alkali electrolytic process consumes 2.10–2.15 kWh of electrical energy and 0.128–0.196 kWh of thermal energy per kg of NaOH produced. The energy efficiency of conventional chlor-alkali processes is around 75%.
While chlor-alkali electrolysis efficiently produces NaOH, it has several drawbacks:
- Significant chlorine gas production as a byproduct. This necessitates specialized and costly equipment for safe handling and monitoring.
- Anode exposure to highly acidic and chloride-rich solutions. This requires expensive stable materials (IrOₓ and/or RuOₓ coated on platinized titanium) for anodes.
These factors contribute to the high capital expenditure associated with chlor-alkali electrolysis plants.
Bipolar membrane electrodialysis employs a stack of cation-exchange membranes, anion-exchange membranes, and bipolar membranes between the cathode and anode to produce NaOH and/or HCl solutions. The bipolar membrane, a key component, consists of two layers: one permeable to protons (H⁺) and the other to hydroxide ions (OH⁻).
The diagram below illustrates a three-chamber bipolar membrane electrodialysis.
When an electric field is applied to a bipolar membrane interface, water molecules dissociate into H⁺ and OH⁻. H⁺ migrates to the acid chamber, while Cl⁻ from the seawater chamber passes through anion-exchange membranes and the electrode solution (ES) to combine with H⁺ in the acid chamber, forming HCl. Simultaneously, OH⁻ moves to the base chamber, where sodium ions (Na⁺) from the seawater chamber traverse cation-exchange membranes to form NaOH.
In general, the energy consumption for a three-chamber bipolar membrane electrodialysis system can range from approximately 1.24 kWh/kg to as high as 17 kWh/kg, depending on the concentration of the produced acids and bases and the efficiency of the system.
The three-chamber bipolar membrane electrodialysis system, however, faces challenges due to its complex membrane configuration. The use of at least five exchange membranes (including two for the bipolar membrane) increases cell resistance. This leads to high operating voltages and low limiting current densities. Consequently, the slow rate of acid and base generation often necessitates the simultaneous operation of multiple systems to maintain usable output feed alkalinity and acidity.
Brineworks has developed an innovative electrolytic electrodialysis technology that can produce NaOH, HCl, and hydrogen gas (H₂) from seawater or brine streams for Direct Ocean Capture (DOC).
Brineworks’s unique electrolytic electrodialysis uses fewer membranes than conventional bipolar membrane electrodialysis. This reduces the electrical resistance and achieves 25 times higher current density, resulting in a higher production rate of HCl and NaOH solutions.
Brineworks’s electrolytic electrodialysis also uses cost-effective Earth-abundant catalysts instead of expensive materials like iridium or ruthenium, produces H₂ byproduct instead of Cl₂, and shows improved stability, making it more economical and environmentally friendly for Direct Ocean Capture (DOC).
The company claims that its technology could bring the cost of carbon capture down to under $100 per ton at scale, significantly lower than the $230 to $630 per ton range typical of Direct Air Capture methods.
How Brineworks produces acid, base, and hydrogen
The diagram below illustrates how Brineworks produces NaOH, HCl, and H₂ via its unique electrolytic electrodialysis technology.